1. Field of the Invention
This invention relates to surgical ligament tensioning apparatus which is particularly, although not exclusively, applicable for use in surgery of the knee and especially total knee arthroplasty.
2. Description of the Prior Art
The surgical goals of knee arthroplasty are relief of pain and restoration of functional mobility of the knee. The key factors in achieving these goals include the maintenance of correct prosthetic alignment, fixation and articulation.
The majority of knees presented for treatment with total knee arthroplasty suffer a ligamentous imbalance which can lead to a decreased range of motion, instability of the implant and increased polyethylene wear if such a material is used in the prosthesis.
During such operations it is therefore necessary to eliminate the passive deforming forces around the knee associated with soft tissue imbalance at the time of surgery. This is achieved by graduated soft tissue release of the contracted tissues around the knee. In order to carry out this technique successfully, the surgeon has to ensure that the knee is symmetrically balanced both medio laterally and between flexion and extension. In the past, this has been done by eye judgment which is difficult, since, if after surgery the knee is imbalanced, then failure of the prosthesis can result.
U.S. Pat. No. 5,468,244 shows a surgical apparatus for use in a tensor based technique for knee surgery which employs first and second tissue engaging means displaceable towards and away from each other. One of the tissue engaging means is arranged to be oriented by the tissue engaged and measuring means are provided to measure displacement between the tissue engaging means and also measure the rotation of the appropriate tissue engaging means so that the imbalance can be corrected by eliminating the necessary soft tissue to ensure that the ligamentous imbalance is corrected prior to the fitting of the prosthesis.
The present invention is intended to provide apparatus which can be used in a tensor based technique and which addresses the critical issues of correction positioning, restoration of the joint's functional mobility and the long term survivorship of the knee prosthesis through improved alignment and greater stability and relies upon an improved construction of the surgical apparatus shown in U.S. Pat. No. 5,468,244.